1. Field of the Invention
This invention relates to a mixture control apparatus for a carburetor, and more particularly to a mixture control apparatus for use in a carburetor of the type having a choke valve on the upstream side and a throttle valve on the downstream side respectively in an intake barrel relative to a venturi section admitting an opening end of a main fuel nozzle, which mixture control apparatus is adapted to control the opening angle of the aforementioned choke valve and throttle valve by means of two cams fixed on one output shaft of an electric motor or on one output shaft of a speed reducer of the electric motor.
More specifically, this invention relates to a mixture control apparatus for a carburetor, constructed so that the movement of an electric motor from the side of reverse rotation thereof past a home position to the side of normal rotation thereof is executed based on the logical multiplication of at least the three conditions:
(1) that the engine temperature should exceed the boundary temperature between the cold state and the hot state, PA1 (2) that the revolution number of the engine should exceed a preset value, and PA1 (3) that the throttle lever should be mechanically separated from the aforementioned second rotary cam,
and, after the engine has been changed to the hot state, the aforementioned electric motor is prevented from moving from the side of normal rotation thereof past the home position to the side of reverse rotation thereof unless a stop of the engine is detected.
2. Description of the Prior Art
It is known to provide a mixture control apparatus for a carburetor comprising a choke valve disposed on the upstream side and a throttle valve on the downstream side respectively in an air inlet relative to a venturi section admitting an opening end of a main fuel nozzle, first rotary cam means interlocked with said choke valve and adapted to operate said choke valve from the totally opened position to the totally closed position thereof, second rotary cam means interlocked with said throttle valve and adapted to operate said throttle valve to a prescribed degree of opening for fast idling, and an electric motor for driving said first and second rotary cam means and determining the rotational positions thereof according to the operating condition of an internal combustion engine, which mixture control apparatus is characterized in that said electric motor is adapted to be rotated in a normal direction and in a reverse direction from a home position thereof as the boundary, that said first and second cam means have the shapes thereof selected so that when said electric motor is rotated in the normal direction from said home position, said choke valve will be retained at a substantially fully opened position and said throttle valve will have the degree of opening thereof increased and, when said electric motor is rotated in the reverse direction from said home position, said choke valve will have the degree of opening thereof decreased and said throttle valve will have the degree of opening thereof increased. The construction of the carburetor part and the construction and operation of an electrical control circuit incorporated therein are described in detail in the specification of Japanese Patent Application SHO 56(1981)-177996, for example.